1. Field of the Invention
The present invention relates to a resin composition for an optical film having excellent heat resistance and optical properties, a polarizer protective film including the same, and a liquid crystal display including the polarizer protective film.
2. Description of the Related Art
Display technologies using various devices replacing a conventional cathode ray tube, such as a plasma display panel (PDP) and a liquid crystal display (LCD), have been developed and have become commercially available on the basis of recent advancements in optical technology. The characteristics of polymer materials in such display devices have become highly advanced. For example, wide viewing angles, high contrast, prevention of changes in image color according to viewing angle, and uniformity of image display have become particularly important issues as liquid crystal displays have become lightweight and have been provided with large-sized picture areas as well as thin films.
A polarizing plate generally has a structure in which a triacetyl cellulose film (hereinafter, referred to as a “TAC film”), as a protective film, is stacked on a polarizer by using a water-based adhesive formed of a polyvinyl alcohol-based aqueous solution. However, both of a polyvinyl alcohol film used as the polarizer and the TAC film used as the protective film for a polarizer may have insufficient resistivity to heat and humidity. Accordingly, when a polarizing plate formed of the foregoing films is used over a prolonged period of time in a high-temperature or high-humidity environment, the polarizability thereof may degrade, the polarizer and the protective film may be separated or the optical properties thereof may deteriorate. Therefore, the foregoing polarizing plate may have various limitations in terms of the usage thereof.
Also, the TAC film has large changes in existing in-plane and thickness retardation values according to changes in an ambient temperature/humidity environment and in particular, changes in a retardation value with respect to incident light in an inclination direction may be large. When a polarizing plate, including a TAC film having the foregoing characteristics, is applied to a liquid crystal display as a protective film, image qualities may deteriorate because viewing angle characteristics may be changed according to changes in an ambient temperature/humidity environment. Further, the TAC film not only has a high dimensional change rate according to changes in an ambient temperature/humidity environment, but also has a relatively large photoelastic coefficient. Therefore, image quality may be easily deteriorated due to the occurrence of local changes in retardation value characteristics after durability evaluation in heat-resistant and moisture-resistant environments.
An acryl-based resin is a well-known material for compensating for various disadvantages of the TAC film. However, the acryl-based resin has insufficient heat resistance, and in-plane and thickness retardation values are generated after drawing. Therefore, the acryl-based resin may not be appropriate to be used as a protective film.